1. Field of the Invention
The present invention is directed to generation of signals by a telephone or other telecommunications device, and more particularly, switching between generating pulse code and dual tone multifrequency signals automatically in response to status of the telephone or signals received by the telephone.
2. Description of the Related Art
For many years telephones have been able to use dual tone multifrequency signals to instruct a switch in a central office of the public switched telephone network what number is to be connected for communications. However, this capability is not universally available and is often an extra charge. All switches are able to respond to older "pulse codes" which were generated by rotary dial telephones. Conventional telephones are available which are capable of generating either pulse codes or dual tone multifrequency (DTMF) signals. Most commonly, internal signals are generated by an input device, such as a three-by-four keypad of numerals 0-9, "*" and "#". Other input devices in common use include four-by-four keypads which add the letters A-D and keypads with the numerals 0-9 arranged in an arc with the appearance of a dial telephone. All conventional telephones which are capable of both pulse code and DTMF signaling include a manual switch to indicate which type of signals will be output from the telephone in response to activation of the keypad or other input device.
There are many types of automated services which are now available by telephone. Examples include voicemail, telephone banking, reservation systems, information services from newspapers, etc. Virtually all such systems rely upon DTMF signals to indicate caller response to audio menus. A small portion rely upon some form of voice signals, e.g., "grunt" detection. However, the vast majority of telephone owners who must, or have chosen to, indicate numbers called by using pulse code signals, have to manually switch to DTMF generation after dialing any of these automated services and then must remember to switch back to pulse code signal generation before calling a different number.